What is mesothelioma?

Mesothelioma (also called malignant mesothelioma) occurs when abnormal cells in the tissue that surrounds the lungs grow in an uncontrolled way.

The lungs are covered by a double layer of tissue called the pleura, which protects and cushions the lungs. The pleura is made up of layer of cells called mesothelium (or mesothelial cells) and connective tissue. Mesothelium also covers the outer surface of most of the body’s other internal organs, including the organs of the abdomen, the heart and the testicles. It makes a lubricating fluid that helps the organs move against each other.

Mesothelioma starts in the mesothelium. About three-quarters of mesotheliomas are in the tissue surrounding the lungs. This is not the same as lung cancer, which starts inside the lungs.

This information on these pages relates mainly to pleural mesothelioma (in the lining of the lungs).